Superheating water tube boiler



y 1936- c. s. TURNER 2,046,349

SUPERHEATING WATER TUBE BOILER Filed Sept. 7, 1934 I 2 sheets-Sheet 1 vINVENTOR. @kaflts 5 fz'zrrzer July 7, 1936. c. s. TURNER SUPERHEATINGWATER TUBE BOILER ,2 Sheets-Sheet 2 Filed Sept. '7, 1954 @lzarles BUPatented Jul 7, 1936 A UNITED I STATES PATENT OFFICE SUPERHEATING WATERTUBE BOILER Charles S. Turner, Detroit, Mich. Application September 1,1934, Serial No. 743,069

'1 Claims. (01. 122-473) This invention relates to superheater bollers,and is directed to the improvement of water tube boilers in general andof the superheater constructions disclosed in my copenclingapplications, Serial Nos. 496,868, filed November 20, 1930, superheaterconstruction", 512,675, filed January 31, 1931,, superheaterconstruction, 534,490, filed May 2, 1931, Fluid cooled superheaterconstruction, 590,108, filed February 1, 1932, "superheater assembly,and 699,541, filed November 24, 1933, superheater construction inparticular.

In marine boilers especially compactness in proportion to steam deliveryis of course important, and they are ordinarily, therefore, not onlyarranged in a compact manner, but operated at a relatively high ratingwhich involves very rapid heat transference. In providing such boilerswith superheater equipment it has heretofore been considered impossibleto subject that equipment to the direct radiant heat from the burners,and superheaters as applied to such boilers have accordingly beencommonly placed in guarded positions remote from the furnace andoperated by convection only. No matter what the type of suchsuperheaters, however, the practice has been to provide special steaminlet headers to which an ofitake from the steam drum of the boiler hasbeen connected by suitable piping. v

An important object of the present invention, therefore, is theprovision of means whereby marine and other water tube boilers may beequipped with superheating apparatus not only of markedly greaterefiiciency than any heretofore available, but which requires the use ofno additional drums, inlet headers, connecting pipe, or other externalaccessories for the superheater other than a water inlet and a take offfor superheated steam, and in which the functions of the eliminatedelements are all' performed by and within the conventional steam drum ofthe boiler itself, and the construction thus rendered more compact thanthose now in use incorporating superheaters.

Still another object is the provision of improved means for controllingradiant superheater elements by partially shielding the same in a novelmanner to limit the quantity of radiant heat to which they are subjectedwithout destroying the substantially proportional accessibility ofvarious portions of the elements to radiant heat.

Other objects and-advantages will be apparent from the followingdescription, wherein reference is made to the accompanying drawingsillustrating preferred embodiments of my invention and wherein similarreference numerals designate similar parts throughout the several views.

In the drawings:

Figure 1 is a vertical sectionalelevation of a marine boiler, shownsomewhat diagrammatically and illustrating a typical application of myinvention.

Figure 2 is an enlarged detailed section of one of the superheaterelements taken substantially on the line 2-2 of Figure 1, and looking inthe direction of the arrows.

Figure 3 is an enlarged and fragmentary vertical section of the lowerportion of a similar boiler incorporating my invention in somewhatmodified form.

Figure 4 is a horizontal section taken substantially on the line 44 ofFigure 3, and

Figure 5 is an enlarged and fragmentary vertical section of the upperportion shown in Figure 4.

Referring now to the drawings, reference character l designatesgenerally the angular banks of water tubes of an A-type marine boiler,which is shown somewhat diagrammatically in the conventionalpartsthereof which are unaifected by addition of my invention, and whichserves merely to exemplify a preferred application of my invention. Thesuperheater comprises a plurality of elements arranged generally paral-.lel to the water tubes l0 and terminating at their upper ends in thesame steam drum 2|. In the embodiment shown .in Figures 1 and 2 thesuperheater elements, generally designated 20, are shown arranged infront of the first row of water tubes and directly exposed to radiantheat.

Each element 20 consists of a unitary assembly of tubes welded togetheras at l8 to provide heat bridges therebetween. In the form showncrosssectionally in Figure 2 the water tubes l are directly welded incircumferentially spaced relation to the surface of the larger centraltube l2 for steam to be superheated. The purpose and proportioning ofthese parts will be discussed in greater detail later. The upperextremity of each of the units 20 thus formed is projected into theupper steam drum 2i of the boiler, in which all are of course sealed. Asuitable water levelis exemplified at 25. The central, superheating tubeI! may project to a point near the top of the drum and well above thewater level, while the cooling tubes I5 preferably terminate at a lowerpoint but also above the water level. Both the tubes l2 and I5 are openat their ends within the drum, but such open ends constitute the outletsof the water tubes l5 and the inlets of the steam tubes l2, Hats, as2621, may be arranged over each, to guard against the undesiredsplashing of water thereinto. At their lower extremities the superheaterassemblies 20 are carried through the sides of the furnace walls 29 andproject therebeyond, a water inlet header, as 30, being provided intowhich the lower ends of water tubes I6 are connected, while thesuperheater tubes l2 terminate in an outlet header 33.

Water is supplied to the water inlet header 30 and so to tubes l5 bymeans of a conduit 3! connecting the header with one of the mud drums,as 40, of the boiler. A throttle valve 36 is arranged in the water inletline 35 for a purpose presently to be described. and is automaticallycontrollable in response to the outlet temperature of the superheatedsteam, as by the thermostatic means diagrammatically represented at 38.A manually operable by-pass valve, as 42, is also provided to enableflooding the water tubes when desired independently of the thermostaticcontrol. For purposes of discussion it may be assumed that during normaloperation the effect of the throttling valve is to maintain the water inthe assembly at a reduced level, although actually, while substantiallyonly water may be present at the bottom ends of the water tubes, andthis condition may exist for only a short distance up the tubes, thereis always some entrained water, even in the zone above what may-betermed the eflective water level, where the steam bubbles have become solarge as to constitute practically the entire content. That is to say,the constantly increasing steam bubble size makes the water levelindefinite, although his none the less real from a practical standpoint,while the presence of entrained water above such theoretical levelaffords the upper part of the assembly a desirable protection by reasonof the'heat absorbing power which although greatly reduced, stillremains therein to some extent.

As shown in Figure 2, the cooling tubes l5 may be arranged only upon theexposed side of each superheater tube l2, since only those areassubjected to radiant heat need the protection thereof, although this isof course a matter of choice. The water tubes l5 and the connectingwelds i8 are so proportioned and positioned that in the area below thetheoretical level, where mainly water is present in the cooling tubes,less than the desired amount of heat can reach the steam within thecentral tube II, the balance being carried away by the water, while whenor where the cooling tubes contain virtually no water or nothing butbubbles, as explained above, the presence of saturated steam and thesmall amount of entrained water therein cannot prevent the properabsorption of heat by the superheating tube l2, and in fact the wallsofthe cooling tubes and the welds then may assist in conducting heat tothe steam tubes.

In operation, steam; is generated in water tubes ID in the normal mannerand delivered to the steam drum 2|. Instead of the usual take-off andconnecting means at the top of the drum. however, the steam leaves thedrum directly through the superheater tubes 12, entering their open topsand flowing downwardly therethrough. During normal operation the steamis superheated while flowing downwardly through the tubes l2, and isthen delivered to the outlet steam header 33, whence it may be conductedto the engines (unshown) or any desired destination. The degree ofsuperheat is regulated byvarying the amount of water in the coolingtubes by throttling its admission to vary the theoretical level and sothe effective length of the superheater unit. This regulation isordinarily eflected automatically by the throttle valve 36, which isthermostatically controlled, as above stated, in reapom to outlet steamtemperature and arranged to decrease the flow and so depress theeffective level when such temperature falls below a desired point, andto open the valve to allow the flow to increase and such level to risewhen the temperature exceeds that point. The water tubes ID, by reasonof their outermost positioning will be seen to act as a screen to limitthe quantity of radiant heat which can reach the steam tube.

When the boiler is first started and no superheated steam is flowing,the valve 36 would normally be closed, and the burners would accordinglyelevate the superheater units to a dangerous temperature if provisionwere not made for flooding the water tubes. Flooding is accomplished tosafeguard the tubes by means of a manually operable by-pass around thethermostatic valve, such as is shown in Figure 1 at 42; By opening theby-pass.valve the water tubes may of course be flooded and maintained sountil steam commences -to flow, after which the bypass may be closed andsteam generation within the tubes I! will quickly reduce the effectivelevel therein to the proper point where it will be held under theautomatic regulation of the thermostatic valve.

The screening function of tubes I5 is highly desirable where boilers areoperated at high ratings involving the extremely rapid heat transfersemployed in marine work, although in boilers operated at lower rates ofheat transfer the screening effect might not be desired, in which eventthe steam tubes might be arranged outermost, and the water tubes in aninner position in which neither they nor the saturated steam thereincould interfere with the impingement of radiant heat against the steamtubes.

The superheater units 20 are ordinarily of such length that in normaloperation the effective water level in tubes I! may be held at arelatively low point. From a practical standpoint the area above suchlevel constitutes the eflective superheating surface. Virtually nosuperheating can take place below the water level, for the parts are soproportioned that substantial equilibrium is maintained in this areaunder normal heat delivery to the exteriors of the units. Thisproportioning and relationship will presently be discussed in greaterdetail. In order to prevent undesired desuperheating of the steam whilepassing through the water-containing portions of the superheaterelements outside the zone of heat absorption, where such equilibriumcould not be maintained if the bridging welds were present,,the welds l8preferably extend only as far as the boundary of the zone ofheat-absorption at the lower end. The absence of the bridging welds inthe area beyond the inner surface of walls 29 so tremendously decreasesthe possible heat flow between the tubes l2|5 as to virtually insulateone from the other, so that no desuperheating can take place.

In Figures 3, 4, and 5 'is shown another embodiment in which each of thesuperheater elements, shown cross sectionally in Figure 4, comprises acentral water tube ii, the external surface of which carries radiallyprojecting helically disposed ribs l8, between which its surface isconcaved to received the externally arranged steam tubes I2', which arefitted thereinto and welded to the tips only of the rib portions of thewater tube, as at l8. This places the steam tubes in a more exposedposition which under some conditions may render external screeningdesirable, as will presently be explained, but achieves importantbenefits in restricting direct heat conduction between the steam andwater tubesand so preventing desuperheating, as will also furtherappear. Each of the superheater units, designated 20', may project atits upper extremity into the steam drum 2| in similar fashion to theembodiment first described. The steam tubes 12' extend to a point nearthe top of the drum, where their open inlet ends are guarded by a hat26, while the central water tube I5 stops at a lower point, though alsoabovethe water level, where it is also guarded by a hat as 21'. Thelatter hat not only guards the cooling tube, but prevents it from sodischarging saturated steam and water that it could enter the steamtubes.

A suitable manner of sealing the units 20 in the lower wall of the steamdmm 2| is also detailed in Figure 5. The sleeve 22 is tightly expandedinto the drum or otherwise sealed in place, and is internallydimensioned to receive the unit 20, which after being fitted thereintois welded thereto as at 24 to completely seal the union.

The steam tubes l2 are shown connected at their lower extremities to amanifold 44, after passing through which the steam is discharged intooutlet header 33', while the water tubes l5 project entirely through themanifold andare connected to water inlet header This header is in turnconnected to the mud drum 40, whence the cooling water supply is derivedas through take-oil pipe 35'. A thermostatically controlled throttlevalve designated 36' is shown arranged to control the water supply toenable regulation of level within the central water channel in responseto output steam temperature as in the embodiment previously described,while the manually operable by-pass, as 42', may be similarly provided.

The length of the ribs [6 and the proportions and positioning of thetubes and of the bridging welds i8 are so calculated (by means wellknown and not necessary to be here detailed) that when and in thoseareas in which principally water is present within the central tube I5,the heat travels from the external surface of the assembly to thecooling water more readily than to the steam within tubes l2. Thistendency of the water within central tube l5 to take the heat from thesurface of the assembly when both water and steam to be superheated arepresent is so calculated that under such conditions, when heat is beingdelivered to the assembly at normal boiler rating, substantialequilibrium is maintained within the units below the water level so thatthe water can extract very little if any heat from the steam tubes,which action is prevented also by the insulating effect of the nonweldedassociation of those interfitting areas of the tubes between the welds.As to these areas, designated it should be noted that some gap is alwaysinvolved even in what is commonly termed metal-to-metal" contact, and atthe temperatures and rates of heat transfer here involved, thisconstitutes actual insulation. The steam tubes accordingly remain atapproximately the same temperature as the steam within them, and nodesuperheating takes place, whereas the xcess radiant heat which but forthe presence of the water would continue to superheat the steam to astill higher temperature is absorbed by the water, and furthersuperheating is thus prevented. It will thus be understood that theefrective superheating area of each unit is that above the eflectivewater level in the central tube l5 thereof, and that such length issubject to variation with the level by the above mentioned throttling ofthe water supply, conformably to the relation between the actual anddesired output temperatures of superheated steam and the rate of steamgeneration in water tube lli'f Not only may the steam temperature bethereby held substantially constant at a desired level, but a furthervirtue of this arrangement is that maintenance of constant output steamtemperature may be eflected throughout the entire range of boileroperation, from zero to maximum delivery.

It will be understood that the operation of the throttle valve issimilar to that of an expansion valve, since below it the pressure isgreater than above by reason of the head of water in the boiler, thepressure in the steam tubes of the superheating elements above the valvebeing less by reason of the reduced quantity of liquid, and the freevaporization of such liquid whichthere takes place. By reason of suchfree boiling of the throttled quantity of water, only gravity tends tohold the water in the bottoms of the steam channels. A sharply definedwater level is thus avoided, and the presence of some entrained waterthroughout the steam tubes .as-

sured.

The tubes l2 are shown as helically coiled only within the zone ofheat-absorption. Their indication in Figure 5 as straight at their upperends within the drum is primarily to clarify that view, although thisarrangement might advantageously be used in practise, since the effectof the intercoiling of the tubes is desired only within the zone ofheating, where it assures substantially equal heat absorption by allsteam tubes, thereby not only working all at the same rating but, whichis more important, eliminating the undesirable raising of some steamtubes to a temperature higher than others, which would otherwise forceundue heating of some in order that the average temperature of the steamdelivered by all might be at a desired point. When coiled in this mannerthere is no necessity of either desuperheating as to any steam tubes, orheating some to a temperature higher than others in order to maintain.the desired average temperature.

As indicated at l8, the welding bridge per-- .bottoms of the units, atthe boundary of the zone of heating, in order that in passing throughthe water-containing areas outside the zone of heat absorption the steammay not be desuperheated.

If, as is advantageous in some boilers, it is desired to reduce thequantity of radiant heat able to-reach the superheater thescreeningeffect of one of the rows of water tubes may be availed of. An improvedmanner of providing such screening is indicated in Figures 3 and 4. Asthere shown, the water tubes of the front row designated I0, areprojected through and positioned in front of the superheater units, andare so staggered as to result in concentric grouping thereof about eachunit in a manner imparting a wavular cross-sectional disposition to thetubes and enabling greater access of radiant heat to the superheaterunits than ability of such heat, which is of course propagated only instraight lines, to enter in wide angles and so impinge virtually theentire surface, as diagrammatically indicated by the arrows designated89.

While it will be apparent that the illustrated embodiments of myinvention herein disclosed are well calculated to adequately fulfill theobjects and advantages primarily stated, it is to be understood that theinvention is susceptible to variation, modification and change withinthe spirit and scope of the subjoined claims.

What I claim is:

1. In combination with a boiler having watercontaining steam generatingportions arranged in a zone of heat absorption, and a collectingreceptacle for saturated steam arranged thereabove and having a. waterlevel therein, a water regulated superheater assembly arranged in thezone of heat absorption and incorporating a water control conduit and asuperheater conduit integrated therewith to form a unitary assembly, thesuperheater conduit having an inlet end portion projecting into saidreceptacle and above the water level to receive therefrom steam to besuperheated, and the watercontrol conduit having an outlet therein alsoabove the water level.

2. In combination with a boiler having water tubes for generatingsaturated steam arranged within a zone of heat absorption and having acollecting drum to which the upper ends of said tubes are connected andwithin which a water level is normally maintained, a water regulatedsuperheater assembly arranged within the zone of heat absorption andincorporating a superheating tube and a water-control tube integratedtherewith to form a unitary assembly, the water-control tube beingadapted to generate saturated steam, controllable means for feedingwater to the lower end of said watercontrol tube, said assembly beingprojected and sealed into the drum at its upper end and thesuperheating' tube having an open inlet end near the top thereof andabove the water level, and the water-control tube having an open outletend also within' the drum and above the water level, whereby a reducedwater level may be held in the cooling conduit.

3. In combination with a boiler having water tubes for generatingsaturated steamv arranged within a zone of heating, a collecting drum towhich the upper ends of said tubes are connected and within which awater level is normally maintained, and a flooded drum to which thelower ends of said generating tubes are connected, a water cooledsuperheater assembly arranged within the zone of heating andincorporating at least one superheating tube and at least one coolingtube, the latter adapted to generate saturated steam, said tubes beingintegrated to form a unitary assembly and arranged generally parallel tothe generating tubes and connected to the collecting drum, thesuperheating tube having an inlet at its upper extremity projecting to apoint near the top of the drum and above the water level, the coolingtube having an outlet portion at its upper extremity also projectingwithin the drum to a position above the water level, and said tubeshaving an outlet and an inlet respectively at their lower ends,including controllable means for feeding water to the cooling tube fromsaid flooded drum. 7

4. In combination with a boiler having water tubes arranged within azone of heating and bounding a zone of radiant heat, a collecting l drumto which the upper ends of said tubes are connected and within which awater level is normally maintained, and. a flooded drum to which thelower ends of saidgenerating tubes are connected, a water regulatedsuperheater as- I0 sembly arranged in the path of radiant heat andincorporating regulating and superheating tubes integrated throughouttheir effective lengths within the zone of heat absorption and connectedto and extending through a lower 15 wall of said collecting drum, thesuperheating tube having a continuation forming an inlet and openingwithin said drum near the top thereof and above the water level, and theregulating tube having an outlet continuation also opening 0 within saiddrum above the water level, controllable means for feeding water to thelower end of the regulating tube, whereby a reduced level may be heldtherein, and means for taking off superheated steam from the lower end25 of the superheating tube.

5. In a steam boiler construction, in combination with a furnace, aboiler including a steam drum, a plurality of water tubes arranged in 1exposed position with respect to radiant heat 30 from the furnace, aplurality of water-regulated superheater elements arranged at an angleto the horizontal and generally parallel to the wa-' ter tubes, aplurality of said water tubes being grouped about each of said elementsin 35 spaced generally circumferential arrangement.

6. In a steam boiler construction, in combination with a furnace, aboiler including a steam drum, a plurality of water tubes connected toand extending downwardly from the bottom of the drum, and a plurality ofwater regulated superheater elements extending into said same drum andeach comprising separate but integrated conduits for steam to besuperheated and for regulating water, each of said conduits having anopening at its end within the drum and above the normal water leveltherein, a shield over each of said openings to guard against splashingthereinto, and means for regulatably admitting cooling water to thebottoms of the regulating conduits in each of said elements.

7. In a steam boiler construction, in combination with a furnace, aboiler including a steam drum, a. plurality of water tubes connected toand extending, downwardly from the bottom of the drum at spaced pointstherealong, anda plurality of water regulated superheater elementsextending upwardly through the bottom of the drum also at spaced pointstherealong and each including separate conduits for steam to 60 besuperheated and for regulating water, said conduits extending upwardlywithin said drum and each having an opening therein above the waterlevel, the opening in the tube for regulating water constituting anoutlet and that in the 65 superheater tube constituting an inlet, theinlet being located above the outlet means for regulatably admittingregulating water to the bottoms of the cooling conduits, and means forguarding said outlets against splashing of water into the 70 regulatingwater conduits.

CHARLES S. TURNER.

